zapaDEV - CSS Filter Generator | Convert from black to target hex color

'use strict';

class Color {
    constructor(r, g, b) {
        this.set(r, g, b);
    }

    toString() {
        return `rgb(${Math.round(this.r)}, ${Math.round(this.g)}, ${Math.round(this.b)})`;
    }

    set(r, g, b) {
        this.r = this.clamp(r);
        this.g = this.clamp(g);
        this.b = this.clamp(b);
    }

    hueRotate(angle = 0) {
        angle = angle / 180 * Math.PI;
        const sin = Math.sin(angle);
        const cos = Math.cos(angle);

        this.multiply([
            0.213 + cos * 0.787 - sin * 0.213,
            0.715 - cos * 0.715 - sin * 0.715,
            0.072 - cos * 0.072 + sin * 0.928,
            0.213 - cos * 0.213 + sin * 0.143,
            0.715 + cos * 0.285 + sin * 0.140,
            0.072 - cos * 0.072 - sin * 0.283,
            0.213 - cos * 0.213 - sin * 0.787,
            0.715 - cos * 0.715 + sin * 0.715,
            0.072 + cos * 0.928 + sin * 0.072,
        ]);
    }

    grayscale(value = 1) {
        this.multiply([
            0.2126 + 0.7874 * (1 - value),
            0.7152 - 0.7152 * (1 - value),
            0.0722 - 0.0722 * (1 - value),
            0.2126 - 0.2126 * (1 - value),
            0.7152 + 0.2848 * (1 - value),
            0.0722 - 0.0722 * (1 - value),
            0.2126 - 0.2126 * (1 - value),
            0.7152 - 0.7152 * (1 - value),
            0.0722 + 0.9278 * (1 - value),
        ]);
    }

    sepia(value = 1) {
        this.multiply([
            0.393 + 0.607 * (1 - value),
            0.769 - 0.769 * (1 - value),
            0.189 - 0.189 * (1 - value),
            0.349 - 0.349 * (1 - value),
            0.686 + 0.314 * (1 - value),
            0.168 - 0.168 * (1 - value),
            0.272 - 0.272 * (1 - value),
            0.534 - 0.534 * (1 - value),
            0.131 + 0.869 * (1 - value),
        ]);
    }

    saturate(value = 1) {
        this.multiply([
            0.213 + 0.787 * value,
            0.715 - 0.715 * value,
            0.072 - 0.072 * value,
            0.213 - 0.213 * value,
            0.715 + 0.285 * value,
            0.072 - 0.072 * value,
            0.213 - 0.213 * value,
            0.715 - 0.715 * value,
            0.072 + 0.928 * value,
        ]);
    }

    multiply(matrix) {
        const newR = this.clamp(this.r * matrix[0] + this.g * matrix[1] + this.b * matrix[2]);
        const newG = this.clamp(this.r * matrix[3] + this.g * matrix[4] + this.b * matrix[5]);
        const newB = this.clamp(this.r * matrix[6] + this.g * matrix[7] + this.b * matrix[8]);
        this.r = newR;
        this.g = newG;
        this.b = newB;
    }

    brightness(value = 1) {
        this.linear(value);
    }

    contrast(value = 1) {
        this.linear(value, -(0.5 * value) + 0.5);
    }

    linear(slope = 1, intercept = 0) {
        this.r = this.clamp(this.r * slope + intercept * 255);
        this.g = this.clamp(this.g * slope + intercept * 255);
        this.b = this.clamp(this.b * slope + intercept * 255);
    }

    invert(value = 1) {
        this.r = this.clamp((value + this.r / 255 * (1 - 2 * value)) * 255);
        this.g = this.clamp((value + this.g / 255 * (1 - 2 * value)) * 255);
        this.b = this.clamp((value + this.b / 255 * (1 - 2 * value)) * 255);
    }

    hsl() {
        // Code taken from https://stackoverflow.com/a/9493060/2688027, licensed under CC BY-SA.
        const r = this.r / 255;
        const g = this.g / 255;
        const b = this.b / 255;
        const max = Math.max(r, g, b);
        const min = Math.min(r, g, b);
        let h, s, l = (max + min) / 2;

        if (max === min) {
            h = s = 0;
        } else {
            const d = max - min;
            s = l > 0.5 ? d / (2 - max - min) : d / (max + min);
            switch (max) {
                case r:
                    h = (g - b) / d + (g < b ? 6 : 0);
                    break;

                case g:
                    h = (b - r) / d + 2;
                    break;

                case b:
                    h = (r - g) / d + 4;
                    break;
            }
            h /= 6;
        }

        return {
            h: h * 100,
            s: s * 100,
            l: l * 100,
        };
    }

    clamp(value) {
        if (value > 255) {
            value = 255;
        } else if (value < 0) {
            value = 0;
        }
        return value;
    }
}

class Solver {
    constructor(target, baseColor) {
        this.target = target;
        this.targetHSL = target.hsl();
        this.reusedColor = new Color(0, 0, 0);
    }

    solve() {
        const result = this.solveNarrow(this.solveWide());
        return {
            values: result.values,
            loss: result.loss,
            filter: this.css(result.values),
        };
    }

    solveWide() {
        const A = 5;
        const c = 15;
        const a = [60, 180, 18000, 600, 1.2, 1.2];

        let best = {loss: Infinity};
        for (let i = 0; best.loss > 25 && i < 3; i++) {
            const initial = [50, 20, 3750, 50, 100, 100];
            const result = this.spsa(A, a, c, initial, 1000);
            if (result.loss < best.loss) {
                best = result;
            }
        }
        return best;
    }

    solveNarrow(wide) {
        const A = wide.loss;
        const c = 2;
        const A1 = A + 1;
        const a = [0.25 * A1, 0.25 * A1, A1, 0.25 * A1, 0.2 * A1, 0.2 * A1];
        return this.spsa(A, a, c, wide.values, 500);
    }

    spsa(A, a, c, values, iters) {
        const alpha = 1;
        const gamma = 0.16666666666666666;

        let best = null;
        let bestLoss = Infinity;
        const deltas = new Array(6);
        const highArgs = new Array(6);
        const lowArgs = new Array(6);

        for (let k = 0; k < iters; k++) {
            const ck = c / Math.pow(k + 1, gamma);
            for (let i = 0; i < 6; i++) {
                deltas[i] = Math.random() > 0.5 ? 1 : -1;
                highArgs[i] = values[i] + ck * deltas[i];
                lowArgs[i] = values[i] - ck * deltas[i];
            }

            const lossDiff = this.loss(highArgs) - this.loss(lowArgs);
            for (let i = 0; i < 6; i++) {
                const g = lossDiff / (2 * ck) * deltas[i];
                const ak = a[i] / Math.pow(A + k + 1, alpha);
                values[i] = fix(values[i] - ak * g, i);
            }

            const loss = this.loss(values);
            if (loss < bestLoss) {
                best = values.slice(0);
                bestLoss = loss;
            }
        }
        return {values: best, loss: bestLoss};

        function fix(value, idx) {
            let max = 100;
            if (idx === 2 /* saturate */) {
                max = 7500;
            } else if (idx === 4 /* brightness */ || idx === 5 /* contrast */) {
                max = 200;
            }

            if (idx === 3 /* hue-rotate */) {
                if (value > max) {
                    value %= max;
                } else if (value < 0) {
                    value = max + value % max;
                }
            } else if (value < 0) {
                value = 0;
            } else if (value > max) {
                value = max;
            }
            return value;
        }
    }

    loss(filters) {
        // Argument is array of percentages.
        const color = this.reusedColor;
        color.set(0, 0, 0);

        color.invert(filters[0] / 100);
        color.sepia(filters[1] / 100);
        color.saturate(filters[2] / 100);
        color.hueRotate(filters[3] * 3.6);
        color.brightness(filters[4] / 100);
        color.contrast(filters[5] / 100);

        const colorHSL = color.hsl();
        return (
            Math.abs(color.r - this.target.r) +
            Math.abs(color.g - this.target.g) +
            Math.abs(color.b - this.target.b) +
            Math.abs(colorHSL.h - this.targetHSL.h) +
            Math.abs(colorHSL.s - this.targetHSL.s) +
            Math.abs(colorHSL.l - this.targetHSL.l)
        );
    }

    css(filters) {
        function fmt(idx, multiplier = 1) {
            return Math.round(filters[idx] * multiplier);
        }

        return `filter: invert(${fmt(0)}%) sepia(${fmt(1)}%) saturate(${fmt(2)}%) hue-rotate(${fmt(3, 3.6)}deg) brightness(${fmt(4)}%) contrast(${fmt(5)}%);`;
    }
}

function hexToRgb(hex) {
    // Expand shorthand form (e.g. "03F") to full form (e.g. "0033FF")
    const shorthandRegex = /^#?([a-f\d])([a-f\d])([a-f\d])$/i;
    hex = hex.replace(shorthandRegex, (m, r, g, b) => {
        return r + r + g + g + b + b;
    });

    const result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex);
    return result
        ? [
            parseInt(result[1], 16),
            parseInt(result[2], 16),
            parseInt(result[3], 16),
        ]
        : null;
}

$(document).ready(() => {
    $('button.execute').click(() => {
        const rgb = hexToRgb($('input.target').val());
        if (rgb.length !== 3) {
            alert('Invalid format!');
            return;
        }

        const color = new Color(rgb[0], rgb[1], rgb[2]);
        const solver = new Solver(color);
        const result = solver.solve();

        let lossMsg;
        if (result.loss < 1) {
            lossMsg = 'This is a perfect result.';
        } else if (result.loss < 5) {
            lossMsg = 'The is close enough.';
        } else if (result.loss < 15) {
            lossMsg = 'The color is somewhat off. Consider running it again.';
        } else {
            lossMsg = 'The color is extremely off. Run it again!';
        }

        $('.realPixel').css('background-color', color.toString());
        $('.filterPixel').attr('style', result.filter);
        $('.filterDetail').text(result.filter);
        $('.lossDetail').html(`Loss: ${result.loss.toFixed(1)}. <b>${lossMsg}</b>`);
    });
});